Light producing system

ABSTRACT

A method is provided whereby a high density of metallic atoms may be obtained in the plasma of a flash lamp by deposition of the desired metal substantially uniformly over the inside of an evacuated tube. Applying a pulse of current which vaporizes the metal produces the desired results.

United States Patent Inventor Charles F. Gallo [56] References Cited UNITED STATES PATENTS 1,041,076 10/1912 Hayden 1,837,746 12/1931 Zworykin 1,966,236 7/1934 De Boer 2,167,777 8/1939 Rentsehler 2,545,896 3/1951 Pipkin 2,845,324 7/1958 Heney 2,858,686 11/1958 Roth 3,220,224 11/1965 Baird Primary Examiner-John F. Campbell Assistant Examiner-Richard Bernard Lazarus Attorneys-Albert A. Mahassel and Anthony W. Karambelas 3l6/13X 316/13X 316/7X 316/4X 431/94X 316/26 431/94 431/94 ABSTRACT: A method is provided whereby a high density of metallic atoms may be obtained in the plasma ofa flash lamp by deposition of the desired metal substantially uniformly over the inside of an evacuated tube. Applying a pulse of current which vaporizes the metal produces the desired results.

I i-I I I1I'I1l|l I ll 2 FIG. lc 4 l I, f l l'j l'lll T1 INVENTOR. CHARLES E GALLO ATTORNEY LIGHT PRODUCING SYSTEM BACKGROUND OF THE INVENTION This invention relates to light producing systems and more 5 specifically to a process for obtaining selected spectra.

One of the more common methods utilized to produce a flash lamp involves introducing a selected gas, preferably xenon, into a tube envelope. An energized capacitor is discharged into the tube envelope resulting in a burst of energy imparted to the gas, thereby ionizing and exciting the gas and producing the desired spectra. It is known that at low energy inputs, line spectra are produced which are inefficient,

i.e. the amount of energy required to produce the resulting 1 spectra is quite large compared with the resulting spectra produced. With operating conditions set at room temperature, the materials selected to produce the desired spectra have been gases and not metals. When higher energy levels are imparted to these tubes, the line spectra is somewhat broadened 2 until, at sufficiently high energy levels, continuous spectra are produced. it is often a requirement in xerography, among other branches of technology, to provide and utilize a specific light source so as to maximize utilization of the energy and thereby reduce the requirement. Such a situation also exists in the area of laser technology where it is specifically required to obtain selective spectra which will excite a given laser producing element.

In certain situations, the spectra produced by metallic atoms is required. Therefore, metal, generally in the form of a fine powder, is introduced into these tubes along with a selected gas to provide the required spectra. Metallic iodides were first used because these materials, relative to the pure metal, have a high vapor pressure. Through the proper selection of gas and metallic compound, an approximation to the specific spectrum required in a given process is obtained. However, notwithstanding the utilization of high vapor pressure metallic materials, problems have been experienced in maintaining the metal in the atomic or vapor state. Though in a given situation the spectra produced may be usable, it is only a modification of the gas spectra while the metallic atom spectra alone is preferred.

SUMMARY OF THE INVENTION producing system which overcomes the above noted deficiencies.

Another object of this invention is to provide a novel flash lamp which yields light ofa selected spectra.

Still another object of this invention is to provide a novel process for providing a flash lamp which has better efficiency.

Yet another object of this invention is to provide a novel flash lamp system which contains a high density of metallic atoms in its plasma.

Still again another object of this invention is to provide a novel method for emitting controlled spectra.

Yet, still another object of this invention is to provide a better and more efficient light producing system.

The above object and others are accomplished in accordance with the present invention generally speaking by providing an evacuated tube or envelope the inner walls of which are coated with a thin film of the desired metal which produces the desired spectra when vaporized by pulsing with current, thus obtaining the desired results. Thus a light producing system is provided whereby specifically selected spectra may be obtained requiring minimum energy for the production of same.

To manufacture the desired structure a metallic wire of the desired material may be suspended in an evacuated tube suphigh intensity energy is pulsed from the electrodes, through the thin metallic film deposited on the interior of the tube wall, thus vaporizing said metallic film (producing a transparent tube wall) which then emits the spectra of the metallic material. In this manufacturing step it is desirable that the level of energy during the ablation phase be sufficiently high so as to ablate the entire wire. Localized ablation of the wire, which might inhibit ablation of the entire wire, can be avoided by utilizing concepts akin to exploding wire techniques. It is known that in utilizing these techniques, that the entire wire may be ablated, whether or not it is of uniform diameter, if a sufficient amount of energy is imparted to it. The same technique and similar reasoning is applicable to the metallic film deposition on the inner tube walls. In addition, the metallic film depositions may be said to be self-compensating, i.e. where there is a thin layer there is consequently higher resistivity and, therefore, lower current flow so that the power density is approximately the same in the thin areas as in the thick regions. Therefore, when the layer deposited on the interior of the tube walls, consisting of various degrees of thickness, is struck by high intensity energy, substantially the entire film is vaporized.

The case of an exploding wire is to be differentiated from the behavior ensuing from the passage of a low current through an ordinary wire. The controlling factor is the power applied. If the power in a given wire is high enough, the whole wire will be vaporized rather than locally vaporized. When a wire or film is struck with sufi'rciently high energy very quickly, the whole wire or film is ablated. In addition, in a film as opposed to a wire, the current energy can, upon reaching a hole or region of thin metallic film, be avoided by passing around the thin layered section or hole where the resistivity proves to be extremely high.

If, in the method employed above to manufacture the tube, a continuous current carrying path is not established after exploding the wire in the tube, a gas may be-irijected into the tube and the arc stricken repetitively in the gas until such a continuous current carrying pathis established in the metallic film. Then the gas can be pumped out. Furthermore, in the manufacturing step, note that a gas may be injected into the tube before the wire is exploded so as to absorb any effects of the thermal shock necessary to establish the continuous current carrying path on the inner tube walls.

In utilizing the present invention, it is preferable to ablate the metallic film completely every cycle in which the arc is stricken thereby producing an instantaneous high intensity light source. Sufficiently high energy levels are employed which supply the required energy to vaporize the metallic film giving due consideration to keeping this energy at a level so as not to reach the rupture point of the tube walls. This is accomplished by applying a suitable safety factor in the construction of the tube. It is noted that the process of the present invention contemplates striking the metallic film coating the inner sur- 5 face of the envelope or tube directly with high intensity energy thereby eliminating the necessity of utilizing an intermediate or buffering gas atmosphere. For a given metal and energy input, the spectral output will depend upon the amount of metal used which determines optical properties of the metal and the resistivity of the film. The time dependence of the optical spectra is determined by the vapor pressure of the metal, its heat capacity, its conductivity, its vaporization temperature, the quantity of metal utilized and the time dependence of the applied power.

The length and diameter of the tube utilized to practice the invention are not particularly critical parameters and may vary over a wide range. The wall thickness, however, ordinarily will be fairly thick so as to add strength to the tube to protect against the shock wave bombardment. Depending upon the particular energy level at which the system is operable, the wall thickness of the tube may vary in a range of from about I mm. to l0 mm. and preferably, in order to minimize the chance of shattering the tube the thickness will be on the thick side. The material of construction of the tube may be selected from a wide variety of suitable materials. Typical materials utilized for tube construction include quartz, various glasses, Vycor produced by Corning, alkali metal resistant glasses, Lucalux (aluminum oxide Al O polycrystalline material manufactured by G. E.), Yttralux (manufactured by G. E.), and sapphire (aluminum oxide A1 single crystalline form).

The shape of the electrodes utilized in conjunction with the above invention is not particularly critical, however, the size generally should be kept to a minimum and the amount of the protrusion of the electrodes into the tube slight so as to allow condensation of the metallic atoms behind the electrodes in the tube. The material of construction of the electrodes may be selected from a wide variety of suitable materials. Refractory metals are generally the preferred material in order to obtain optimum results. Typical materials include tungsten, molybdenum, niobium and tantalum. The configuration and spacing of the electrodes is not particularly critical and for the most part depends on the size and shape of the tube.

V, Any suitable metal may be used in the practice of the process of the present invention. Metals possessing a high vapor pressure and low vaporization temperatures are particularly preferred because of the low amount of energy necessary to vaporize them. Typical such materials include zinc, gallium, indium, thallium, lead, bismuth, tin, mercury, cadmium, metallic alloys and metallic compounds thereof. With due consideration given to the amount of energy required for vaporization, other metals may be used in the practice of the invention. In addition, lithium, sodium, rubidium, cesium, and potassium may be considered for use if the proper envelope materials are taken to protect against corrosion effect when using these corrosive metals. The metals selectedl would, of course, be dictated by the spectral output required for the particular adaptation of the invention.

The general nature of the invention having been disclosed, the particulars and specifics of the system of the present invention will be more clearly understood by reference to the following drawings ofwhich:

FlG. la-c illustrate a time sequence followed in producing the lamp system of the present invention.

FIG. 2ac illustrate the cyclic operation of the lamp system of the present invention.

In FIG. la is seen a tube envelope I having refractory metallic electrodes 2 sealed into the tube at each end and a metallic wire 3 strung between the refractory metallic electrodes 2. In FIG. Ia a current generating means 4 is applied across these electrodes after the tube has been evacuated thereby instantaneously vaporizing and/or ablating the strung wire. In FIG. Ic, the current generating system is disconnected and the vaporized metal is allowed to coat the tube walls and form an electrically continuous path between the two electrodes. As previously mentioned, if a continuous electrical path does not develop upon initially ablating the strung wire, an arc may be struck again until such a condition is produced with the addition of gas, if desired, to cushion the shock waves produced. If employed, the gas is then removed by conventional evacuation techniques through one of the electrodes having a passage for the gas as shown.

In FIG. 2a is seen the tube envelope 1 as previously described with the continuous current carrying path 5 developed between the electrodes 2. In FIG. 2b, a current pulse is provided across the electrodes from a conventional current generating system not shown causing current to flow through the metallic film connecting the electrodes resulting in the instantaneous vaporization and/or ablation of the metallic film 5. The hot metallic gas is seen to fill the tube volume and emit light. In FIG. 20, the current generating system is disconnected from the tube allowing the metallic gas to cool and recondense on the tube walls forming a continuous electrical path between the electrodes 2 so that the lamp is now ready to be recycled and reignited.

4 DESCRIPTION OF THE PREFERRED EMBODIMENTS To further define the specifics of the present invention the following examples are intended to illustrate and not limit the particulars of the present system. Parts and percentages are by weight unless otherwise indicated. The energy (voltage) in the capacitor may be varied so as to yield various modifications of the metallic spectra line, continuum or intermediate modifcations thereof).

EXAMPLE I A tube of Lucalux material manufactured by G. E. Company, about I5 cm. in length, about 0.5 cm. internal diameter and about 1.5 cm. outside diameter, containing two electrodes is provided. The pointed electrodes, about 0.2 cm. in diameter are constructed of niobium metal and protrude into the tube about 0.3 cm. Sodium metal is distilled into the tube in a quantity of about 23 mg. The lamp is evacuated, sealed and placed in an isothermal oven at about 700 C. and then very slowly cooled until a continuous current carrying path is established within the tube. The resistance of the uniform sodium film is about 4X10" ohms. The 15 microfarad capacitor is energized and discharged into the tube thus vaporizing the metallic deposition on the inner tube walls resulting in the desired spectra.

EXAMPLE II A tube is constructed of quartz material having a length of about 10 cm. and a diameter of about 0.4 cm. internal diameter and about 1.5 cm. outside diameter enclosing two electrodes spaced about 9.6 cm. apart. The pointed electrodes are constructed of tungsten material and protrude into the inner tube about 0.2 cm. A wire of thallium metal 0.45 mm. in diameter is suspended between the electrodes. The tube is then evacuated. A 10 microfarad capacitor is charged up and then discharged to the electrode thereby ablating the wire and resulting in a condensation of metallic atoms all over the inside of the tube walls. The capacitor is then energized and discharged into the tube thereby vaporizing the metallic deposition of the inner walls resulting in the desired spectra.

Although the present examples were specific in terms of conditions and materials used, any of the above listed typical materials may be substituted when suitable in the above examples with similar results. In addition to the steps used to carry out the process of the present invention, other steps or modifications may be used if desirable. For example, a combination of metals or of metals and their compounds may be used to provide any one of a number of desired spectra. A wide variety of specially treated glasses and plastics may be used in constructing the tube envelope. Other methods may be used in constructing the tube and practicing the invention comprising a solid solution of two or more metals or their compounds ablated within the tube to provide the desired metallic deposition on the inner tube walls. In addition, other materials may be incorporated in the tube walls or electrodes which will enhance, synergize or otherwise desirably affect the properties of the systems for their present use. For example, a buffering gas which desirably modifies the metallic spectra may be introduced to absorb the shock produced by vaporization of the metallic material.

Other modifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of the invention.

What is claimed is:

I. The process of providing selected spectra comprising suspending a wire of metallic composition between two electrodes in a tube, passing a current into and through said suspended wire thereby vaporizing said wire in a manner so as to deposit a film of said metal on the inner wall of said envelope and form a conductive path between said electrodes, and pulsing a current through said film causing vaporization and producing the desired spectra.

2. The process as disclosed in claim 1 wherein said metallic substance is selected from at least one member of the group consisting of indium, gallium, thallium, zinc, lead, bismuth. strontium, francium, ytterbium, radium. barium, europium, calcium, magnesium, tin, mercury, cadmium, lithium, sodium, potassium, rubidium, and cesium.

3, The process of producing a high intensity of metallic atoms in a plasma comprising introducing a metallic wire between two electrodes contained in an evacuated envelope, passing high-intensity energy through said wire thereby -fonning a substantially uniform film of said metal on the inner surface of said envelope to fonn a conductive path between said electrodes and vaporizing said metal from the wall so as to emit the desired spectra.

metal is readily 

1. The process of providing selected spectra comprising suspending a wire of metallic composition between two electrodes in a tube, passing a current into and through said suspended wire thereby vaporizing said wire in a manner so as to deposit a film of said metal on the inner wall of said envelope and form a conductive path between said electrodes, and pulsing a current through said film causing vaporization and producing the desired spectra.
 2. The process as disclosed in claim 1 wherein said metallic substance is selected from at least one member of the group consisting of indium, gallium, thallium, zinc, lead, bismuth, strontium, francium, ytterbium, radium, barium, europium, calcium, magnesium, tin, mercury, cadmium, lithium, sodium, potassium, rubidium, and cesium.
 3. The process of producing a high intensity of metallic atoms in a plasma comprising introducing a metallic wire between two electrodes contained in an evacuated envelope, passing high-intensity energy through said wire thereby forming a substantially uniform film of said metal on the inner surface of said envelope to form a conductive path between said electrodes and vaporizing said metal from the wall so as to emit the desired spectra.
 4. The process as described in claim 3 wherein the metallic composition is a pure metal.
 5. The process as described in claim 3 wherein said metal is selected from at least one member of the group consisting of indium, gallium, thallium, mercury, sodium, potassium, strontium, ytterbium, radium, barium, europium, calcium, magnesium, lithium, rubidium, cesium, zinc lead, bismuth, tin and cadmium.
 6. The process of claim 3 wherein the metal is one possessing a high vapor pressure.
 7. The process of claim 3 wherein said metal is readily vaporizable. 